Electromagnetic actuator

ABSTRACT

An object is to provide an electromagnetic actuator that is highly resistant to corrosion and also capable of having high suction power, even in a condition where part of the electromagnetic actuator touches a corrosive liquid. An electromagnetic actuator  50  according to this invention is incorporated into a device using a corrosive liquid  17 . The electromagnetic actuator  50  is characterized by including a magnetic pole piece  1 ; an outer yoke  6 ; a bottom yoke  5 ; a bobbin coil  2 ; a stepped portion  6   a  that is formed on an outer surface of the outer yoke  6 ; a waterproof portion  8  that prevents the corrosive liquid  17  from entering at least where the bobbin coil  2  and the magnetic pole piece  1  are; a movable plate  12  that is placed in the corrosive liquid  17  to form a magnetic circuit together with the magnetic pole piece  1 , the outer yoke  6 , and the bottom yoke  5 , The movable plate  12  is stored in a space  14  created either in the electromagnetic actuator  50  or between the device using the corrosive liquid  17  and the electromagnetic actuator  50 . The outer yoke  6  is incorporated into the device using the corrosive liquid  17 , on a reduced diameter side from the stepped portion  6   a.

TECHNICAL FIELD

The present invention relates to an electromagnet that is used in aspecific environment, such as in a corrosive liquid, and thereforerequires resistance to corrosion.

BACKGROUND ART

An electromagnet, which is characterized by having a two-piece yoke towhich a nonmagnetic substance is stuck fast and held, and forming a pairof magnetic poles, has been proposed (see, e.g., Patent Document 1). Theelectromagnet is designed to separate a coil portion from harmfulsurroundings, and also work as an electromagnetic by dividing the yokeinto two portions with the nonmagnetic substance that is stuck fast andheld.

A magnetic core, which forms a magnetic circuit in part of a magneticpath, has been proposed (see, e.g., Patent Document 2). The magneticcore consists of magnetic composite material portions and a highmagnetic flux density material portion. The magnetic composite materialportions are formed of magnetic composite materials that are placed onboth end sides of the magnetic circuit. The high magnetic flux densitymaterial portion is formed of a high magnetic flux density materialhaving a higher magnetic flux density and a lower specific resistancethan those of the magnetic composite material portions. The highmagnetic flux density material portion is tightly sandwiched between themagnetic composite material portions in the direction of the magneticpath of the magnetic circuit.

A plunger, which includes a coil bobbin, a coil, and a yoke, and inwhich a resin is poured between the yoke and the coil bobbin appliedwith the coil, has been proposed (see, e.g., Patent Document 3). Theplunger is formed as follows: The diameter W2 of a second flange is setsmaller than the diameter W1 of a first flange (W1>W2). The secondflange is disposed on an open end side of the yoke, and the coil iswound between the first and second flanges in a tapered shape.

An electromagnetic device having high gain and high phase frequencycharacteristic that is used for an actuator such as a magnetic bearingdevice has been proposed (see, e.g., Patent Document 4). Theelectromagnetic device is provided with a stainless steel that surroundsthe magnetic yoke supporting a target object by magnetic attractionwithout touching it.

-   Patent Document 1: Unexamined Japanese Patent Publication No. Hei    4-208504 (see FIG. 1)-   Patent Document 2: Unexamined Japanese Patent Publication No.    2005-150308 (see FIG. 1)-   Patent Document 3: Unexamined Japanese Patent Publication No. Hei    6-295817 (see FIG. 1)-   Patent Document 4: Unexamined Japanese Patent Publication No. Hei    5421228 (see FIG. 1)

DISCLOSURE OF THE INVENTION

When used in a corrosive liquid environment, however, the conventionalelectromagnetic actuators disclosed in Patent Documents 1-4 are notsufficient enough in terms of waterproof and corrosion resistance.

This invention is directed to solve problems like this. It is an objectto provide an electromagnetic actuator that is highly resistant tocorrosion and also capable of having high suction power, even in acondition where part of the electromagnetic actuator touches a corrosiveliquid.

Means to Solve Problems

An electromagnetic actuator according to this invention may beincorporated into a device using a corrosive liquid. The electromagneticactuator may be characterized by including: a magnetic pole piece in ashape of a pillar; an outer yoke in a shape of a tube that is corrosionresistant, and that is placed around a periphery of the magnetic polepiece; a bottom yoke that connects the magnetic pole piece and one endportion of the outer yoke; a bobbin coil that is attached to themagnetic pole piece, the bobbin coil including a first coil holdingportion, and a second coil holding portion on a bottom yoke side; astepped portion that is formed on an outer surface of the outer yoke tomake a diameter on an opposite side to the bottom yoke smaller than adiameter on the bottom yoke side; a waterproof portion that prevents thecorrosive liquid from entering at least where the bobbin coil and themagnetic pole piece are; a movable plate that is placed in the corrosiveliquid to form a magnetic circuit together with the magnetic pole piece,the outer yoke, and the bottom yoke. The movable plate may be stored ina space created either in the electromagnetic actuator or between thedevice using the corrosive liquid and the electromagnetic actuator. Theouter yoke may be incorporated into the device using the corrosiveliquid, on a reduced diameter side from the stepped portion.

An electromagnetic actuator according to this invention may becharacterized by including: a magnetic pole piece in a shape of apillar; an outer yoke in a shape of a tube that is corrosion resistant,and that is placed around the periphery of the magnetic pole piece; abottom yoke that connects the magnetic pole piece and one end portion ofthe outer yoke; a bobbin coil that is attached to the magnetic polepiece, the bobbin coil including a first coil holding portion, and asecond coil holding portion on a bottom yoke side; a waterproof platethat is attached against an end portion of the magnetic pole piece on anopposite side to the bottom yoke, and formed to create a gap between thefirst coil holding portion and an inner surface of the outer yoke; astepped portion that is formed on an outer surface of the outer yoke tomake a diameter on the opposite side to the bottom yoke smaller than adiameter on the bottom yoke side; a movable plate storage cap in a shapeof a cup that is fitted to the outer surface of the outer yoke on areduced diameter side, attached against another end portion of the outeryoke to create a space between the waterproof plate and the movableplate storage cap, and formed to create an opening on a surface facingthe waterproof plate; a movable plate that is placed in the spacebetween the waterproof plate and the movable plate storage cap; and aresin that is filled in a gap formed between the outer yoke and thewaterproof plate. The reduced diameter side from the stepped portion maybe incorporated into the device using the corrosive liquid.

An electromagnetic actuator according to this invention may becharacterized by including: a magnetic pole piece in a shape of apillar; an outer yoke in a shape of a tube that is corrosion resistant,and that is placed around the periphery of the magnetic pole piece; abottom yoke that connects the magnetic pole piece and one end portion ofthe outer yoke; a bobbin coil that is attached to the magnetic polepiece, the bobbin coil including a first coil holding portion, and asecond coil holding portion on a bottom yoke side; a stepped portionthat is formed on an outer surface of the outer yoke to make a diameteron an opposite side to the bottom yoke smaller than a diameter on thebottom yoke side; a waterproof cap in a shape of a cap that is fitted tothe outer surface of the outer yoke on a reduced diameter side, andattached against another end portion of the outer yoke and an endportion of the magnetic pole piece on the opposite side to the bottomyoke; a movable plate storage cap in a shape of a cup that is fitted toan outer surface of the waterproof cap to create a space between thewaterproof cap and the movable plate storage cap, and formed to createan opening on a surface facing the end portion of the magnetic polepiece on the opposite side to the bottom yoke; and a movable plate thatis placed in the space between the waterproof cap and the movable platestorage cap. The reduced diameter side from the stepped portion may beincorporated into the device using the corrosive liquid.

An electromagnetic actuator according to this invention may becharacterized by including: a magnetic pole piece in a shape of apillar; an outer yoke in a shape of a tube that is corrosion resistant,and that is placed around a periphery of the magnetic pole piece; abottom yoke that connects the magnetic pole piece and one end portion ofthe outer yoke; a bobbin coil that is attached to the magnetic polepiece, the bobbin coil including a first coil holding portion, and asecond coil holding portion on a bottom yoke side; a waterproof platethat is attached against an end portion of the magnetic pole piece on anopposite side to the bottom yoke, and formed to create a gap between thefirst coil holding portion and an inner surface of the outer yoke; astepped portion that is formed on an outer surface of the outer yoke tomake a diameter on the opposite side to the bottom yoke smaller than adiameter on the bottom yoke side; a rustproof cap in a shape of a cupthat is fitted to the outer surface of the outer yoke on a reduceddiameter side, and attached against another end portion of the outeryoke, and formed to include an opening whose diameter is approximatelythe same in size as an inside diameter of the outer yoke; and a movableplate. The reduced diameter side from the stepped portion may beincorporated into the device using the corrosive liquid. The movableplate may be stored in a space created in a lower portion of thewaterproof plate between the device and the electromagnetic actuator.

The electromagnetic actuator according to this invention may becharacterized in that the magnetic pole piece and the bottom yoke areformed of an iron material, and the outer yoke is formed of a stainlesssteal.

The electromagnetic actuator according to this invention may becharacterized in that a cross-sectional area of the outer yoke is largerthan a cross-sectional area of the magnetic pole piece.

The electromagnetic actuator according to this invention may becharacterized in that the outer yoke formed of the stainless steal ispainted.

The electromagnetic actuator according to this invention may becharacterized in that the outer yoke is formed of an iron material andpainted.

The electromagnetic actuator according to this invention may becharacterized by including a spacer that is in a shape of a ring andclosely attached to an end surface of the second coil holding portion ata root of the magnetic pole piece on the bottom yoke side, forpositioning and securing the bobbin coil.

The electromagnetic actuator according to this invention may becharacterized in that the bobbin coil includes a power receiving unitthat supplies power to the second coil holding portion. The powerreceiving unit may be placed in a connection space created between thesecond coil holding portion and the bottom yoke.

The electromagnetic actuator according to this invention may becharacterized in that the power receiving unit includes a terminal blockand two terminal pins that are mounted on the terminal block.

The electromagnetic actuator according to this invention may becharacterized in that the two terminal pins are joined and connected,respectively, with the bobbin coil at a winding start portion and awinding end portion by soldering, etc. that melts a film of the coil.

The electromagnetic actuator according to this invention may becharacterized in that the second coil holding portion includes a hangingportion formed on an outer surface, on which a coil end extending overto the terminal pins is hung.

The electromagnetic actuator according to this invention may becharacterized by including an auxiliary sucking portion that is formedat an end portion of the magnetic pole piece on the opposite side to thebottom yoke to increase an area of the end portion.

The electromagnetic actuator according to this invention may becharacterized in that the auxiliary sucking portion is formed of aring-shaped magnetic material or a disk-shaped magnetic material.

The electromagnetic actuator according to this invention may becharacterized in that a relation La>2Lg is satisfied where La representsa distance between an outside diameter of the auxiliary sucking portionand an(the?) inside diameter of the outer yoke, and Lg represents a gapbetween the movable plate and one of the auxiliary sucking portion andthe magnetic pole piece.

The electromagnetic actuator according to this invention may becharacterized in that the magnetic pole piece, the bottom yoke, and theouter yoke are separate piece parts.

The electromagnetic actuator according to this invention may becharacterized in that the magnetic pole piece and the bottom yoke areformed into one piece part when the magnetic pole piece and the bottomyoke are formed of a same material and the outer yoke is formed of adifferent material.

The electromagnetic actuator according to this invention may becharacterized in that the bottom yoke and the outer yoke are formed intoone piece part when the bottom yoke and the outer yoke are formed of asame material and the magnetic pole piece is formed of a differentmaterial.

The electromagnetic actuator according to this invention may becharacterized in that the magnetic pole piece, the bottom yoke and theouter yoke are formed into one piece part when the magnetic pole piece,the bottom yoke and the outer yoke are formed of a same material.

Effects of the Invention

According to an electromagnetic actuator of this invention, an outeryoke that touches a corrosive liquid is made resistant to, corrosion.Furthermore, the electromagnetic actuator has a waterproof structurewith a proof plate provided at an end portion of a magnetic pole pieceon a movable plate side, by injecting a resin into a gap between theouter yoke and the waterproof plate. This may prevent corrosion. Thus,the electromagnetic actuator may be allowed to reduce its size with highsuction power.

BEST MODE FOR IMPLEMENTING THE INVENTION

Embodiment 1

A first embodiment is described with reference to FIG. 1 to FIG. 6. FIG.1 illustrates a longitudinal section of an electromagnetic actuator 50.FIG. 2 illustrates a transverse section of the electromagnetic actuator50 where a bobbin coil 2 is not shown. FIG. 3 illustrates a longitudinalsection of an iron core where a ring-shaped auxiliary sucking portion 20is additionally attached to a magnetic pole piece 1. FIG. 4 illustratesa longitudinal section of an iron core where a disk-shaped auxiliarysucking portion 20 is additionally attached to the magnetic pole piece1. FIG. 5 illustrates a longitudinal section of the electromagneticactuator 50 having a waterproofing portion formed by a waterproof cap30. FIG. 6 illustrates a longitudinal section of the electromagneticactuator 50 having a movable plate storage portion 16 b formed on ametal case 16.

As shown in FIG. 1, the electromagnetic actuator 50 has a magnetic polepiece 1 of a circular cylindrical shape (an example of a pillar shape)approximately at the center.

The circular cylindrical magnetic pole piece 1 is surrounded by thebobbin coil 2 that is formed by a coil 4 wound around a bobbin 3. Thebobbin 3 is formed to have a first coil holding portion 3 a (on awaterproof plate 9 side, which will be introduced later) and a secondcoil holding portion 3 b (on a bottom yoke 5 side, which will beintroduced later) on both ends, respectively, to hold the coil 4.

The bobbin coil 2 is surrounded by an outer yoke 6 of a cylindricalshape (an example of a tubular shape). The outer yoke 6 is formed tohave a stepped portion 6 a on the outer surface with a reduced diameteron a movable plate 12 side, which will be introduced later.

The bottom yoke 5 connects together the magnetic pole piece 1 and theouter yoke 6 at one end (on a large diameter side). With the example ofFIG. 1, the bottom yoke 5 is integrated into the magnetic pole piece 1.The bottom yoke 5 is formed to include a lead wire outlet portion 7 on aperiphery side to let a lead wire out from the bobbin coil 2.

The magnetic pole piece 1 is provided with a waterproof portion 8 at anend portion on an opposite side to the bottom yoke 5 (on a suctionsurface side). The waterproof portion 8, which will be introduced later,is formed to include the waterproof plate 9 and a resin 10.

The disk-shaped movable plate 12 is placed facing an end surface of thewaterproof plate 9 in the waterproof portion 8 with a gap 11 in between.

A cup-shaped movable plate storage cap 13 is provided to store themovable plate 12. The movable plate storage cap 13 is fitted to theouter surface of the outer yoke 6 on the reduced diameter side, and alsoattached against an end portion of the outer yoke 6 on the movable plate12 side. This creates a space 14 between the movable plate storage cap13 and the waterproof plate 9. The movable plate storage cap 13 is thenformed to include a liquid flow inlet portion 15 (an opening) on asurface facing the waterproof plate 9.

The electromagnetic actuator 50 is incorporated into the metal case 16(a housing of a device using corrosive liquid) having an opening 16 ainto which the actuator 50 is fitted on the reduced diameter side. Theelectromagnetic actuator 50 is hermetically sealed and firmly fixed atthe opening 16 a of the metal case 16 by press fitting, shrink fitting,adhesive fitting, or any combinations of those fittings. Theelectromagnetic actuator 50 serves to act as a sealing plug for themetal case 16.

The metal case 16 is filled with a corrosive liquid 17. Theelectromagnetic actuator 50 is brought into contact with the corrosiveliquid on the reduced diameter side (outer surface) from the border ofthe stepped portion 6 a.

As described earlier, the electromagnetic actuator 50 is formed to havethe stepped portion 6 a on the outer surface so that the diameter of thesuction surface side is reduced. The insertion of the electromagneticactuator 50 into the metal case 16 on the reduced diameter side throughthe opening 16 a may result in ensuring the positioning and securing ofthe electromagnetic actuator 50.

The magnetic pole piece 1 and the outer yoke 6 are formed of magneticmaterials of different properties. The magnetic pole piece 1 thatgenerates primary magnetic flux may be formed of an iron material withhigh permeability, such as a carbon steel. The outer yoke 6, on theother hand, may be formed of a ferritic stainless steel (e.g., JISSUS430, SUS405, SUS434, etc.) or a martensitic stainless steel (e.g.,JIS SUS403, SUS410, etc.) that is highly resistant to corrosion withpermeability lower than the magnetic pole piece 1.

The outer yoke 6 thus formed with permeability lower than the magneticpole piece 1 may allow for sufficient suction power while preventing theincrease of inductance, and improving the rising characteristic of anelectric current. This may also allow the electromagnet actuator 50 tobe highly corrosion resistant for use in a specific environment such asin a corrosive liquid.

As shown in FIG. 2, the outer yoke 6 is formed to make a cross-sectionalarea S2 of a magnetic path larger than a cross-sectional area S1 of amagnetic path of the magnetic pole piece 1. This may improve therigidity of the electromagnetic actuator 50. This may also serve tocompensate the reduction in permeability by the increase of thecross-sectional area of the outer yoke 6, thereby achieving highersuction power.

As shown in FIG. 3, the magnetic pole piece 1 may be formed with anauxiliary sucking portion 20 at an end portion on the movable plate 12side. The auxiliary sucking portion 20 is formed of a ring-shapedmagnetic material, which is a part separated from the magnetic polepiece 1. The auxiliary sucking portion 20 is secured to the magneticpole piece 1 by press fitting, adhesive fitting, etc. With the use ofthe auxiliary sucking portion 20, the area of the end portion of themagnetic pole piece 1 on the movable plate 12 side becomes larger, whichresults in increasing the suction power of the electromagnetic actuator50.

When a relation La>2Lg is satisfied, then the suction power of theelectromagnetic actuator 50 may be increased efficiently, where Larepresents a distance between the outside diameter of the auxiliarysucking portion 20 and the inside diameter of the outer yoke 6, and Lgrepresents a gap between the end portion of the auxiliary suckingportion 20 or the magnetic pole piece 1 and the movable plate 12.

As shown in FIG. 4, the auxiliary sucking portion 20 may also be formedin the shape of a disk. The disk-shaped auxiliary sucking portion 20 issecured to the magnetic pole piece 1 at the end portion by adhesivefitting, etc. This may achieve similar effects to those of the auxiliarysucking portion 20 shown in FIG. 3.

The auxiliary sucking portion 20 may also be formed of a ring-shapedmagnetic material (see FIG. 3) or a disk-shaped magnetic material (seeFIG. 4), which is a separate part from the magnetic pole piece 1.Alternatively, the auxiliary sucking portion 20 may be formed into themagnetic pole piece 1.

When the auxiliary sucking portion 20 and the magnetic pole piece 1 areseparate parts, they are firmly fixed to each other by press fitting,adhesive fitting, etc, thereby allowing the bobbin coil 2 to be firmlyfixed.

Needless to say, but similar effects may also be obtained when theauxiliary sucking portion 20 and the magnetic pole piece 1 are formedinto one piece.

When the auxiliary sucking portion 20 is a separate part, the auxiliarysucking portion 20 may be formed of a magnetic material withpermeability higher than the magnetic pole piece 1, thereby allowing theelectromagnetic actuator 50 to increase suction power more efficiently.

As aforementioned, the outer yoke 6 is formed of a ferritic stainlesssteel or a martensitic stainless steel, whose permeability is smallerthan that of the magnetic pole piece 1, and which is highly resistant tocorrosion. Alternatively, the outer yoke 6 may be formed of an ironmaterial such as a carbon steel, and then painted. This may ensure thecorrosion resistance of the electromagnetic actuator 50 in the corrosiveliquid 17 and increase the suction power. In this case, thecross-sectional area S2 of the magnetic path of the outer yoke 6 may bemade smaller than the cross-sectional area S1 of the magnetic path ofthe magnetic pole piece 1 in a range where magnetic saturation does notoccur, thereby allowing the electromagnetic actuator 50 to be downsized.

Alternatively, the magnetic pole piece 1, the bottom yoke 5, and theouter yoke 6 may be formed of a magnetic stainless steel according tothe degree of suction power required for the electromagnetic actuator50. This may allow the electromagnetic actuator 50 to have moreefficient bearing force when it is incorporated into a device using thecorrosive liquid 17.

Alternatively, the magnetic pole piece 1, the bottom yoke 5, and theouter yoke 6 may also be formed of separate piece parts.

When the magnetic pole piece 1 and the bottom yoke 5 are formed of thesame material, and the outer yoke 6 is formed of a different material,then the magnetic pole piece 1 and the bottom yoke 5 may be integratedinto a one-piece part (see the example of FIG. 1).

When the bottom yoke 5 and the outer yoke 6 are formed of the samematerial, and the magnetic pole piece 1 is formed of a differentmaterial, then the bottom yoke 5 and the outer yoke 6 may be integratedinto a one-piece part.

When the magnetic pole piece 1, the bottom yoke 5, and the outer yoke 6are formed of the same material, then the magnetic pole piece 1, thebottom yoke 5, and the outer yoke 6 may be integrated into a one-piecepart.

These parts may be produced easily by hammering, molding, drawing,cutting, etc. selected arbitrarily.

The use of the one-piece part of the magnetic pole piece 1 and thebottom yoke 5, the one-piece part of the bottom yoke 5 and the outeryoke 6, or the one-piece part of the magnetic pole piece 1, the bottomyoke 5, and the outer yoke 6 may allow the electromagnetic actuator 50to be highly rigid and vibration resistant. This may also allow for thereduction in the process of assembly, thereby increasing theproductivity of the electromagnetic actuator 50.

As shown in FIG. 1, the bobbin coil 2 includes the bobbin 3 and the coil4. The bobbin 3 includes a cylindrical coil wound portion 3 c aroundwhich coil is put, the first coil holding portion 3 a (on the suctionside), and the second coil holding portion 3 b (on the bottom yoke 5side). The first and second coil holding portions 3 a and 3 b arespool-shaped and placed on both ends of the coil wound portion 3 c,respectively, and whose outside diameters are larger than the diameterof the coil wound portion 3 c.

The coil 4 is formed by putting a wire around the coil wound portion 3 cof the bobbin 3 with a predetermined number of turns in an arrangedmanner.

The second coil holding portion 3 b on the bottom yoke 5 side of thebobbin coil 2 includes a power receiving unit 21 to supply power to thecoil 4. The power receiving unit 21 is formed to include a terminalblock 22 and terminal pins 23. Wire connection is done in a connectionspace 24 created between the second coil holding portion 3 b of thebobbin 3 and the bottom yoke 5.

The terminal block 22 mounted on an end surface of the second coilholding portion 3 b is incorporated into the second coil holding portion3 b. The terminal block 22 has two of the terminal pins 23 mountedthereon. A wiring start portion and a wiring end portion of the coil 4are wrapped around the terminal pins 23, respectively. The wiring startportion and the wiring end portion of the coil 4 are joined andconnected with the terminal pins 23 by soldering, etc. that melts theinsulting film of the wire.

The second coil holding portion 3 b is formed to include a hangingportion (not shown) on the periphery thereof. The hanging portion isused for hanging a coil end (not shown) that extends over to theterminal pins 23 from the coil 4. This makes wrapping easy. This alsoserves to prevent the coil end from extending outside to meet the insidediameter of the outer yoke 6.

The lead wire outlet portion 7 is a cutout or an opening formed in thevicinity of the outer surface of the bottom yoke. The lead wire outletportion 7 may allow for an easy drawing of a lead wire (not shown)outside via the power receiving unit 21 on the bobbin coil 2.

The cutout or opening is formed in the vicinity of the outer surface ofthe bottom yoke 5 where the cross-sectional area is larger than that ofa central portion of the bottom yoke 5, thereby ensuring a magnetic pathfor acquiring suction power. This may prevent a reduction in suctionpower caused by magnetic saturation.

A spacer 25 of a ring shape is applied at the root of the magnetic polepiece 1 (on the bottom yoke 5 side). The bobbin coil 2 is positioned andsecured by the spacer 25 closely attached to the end surface of thesecond coil holding portion 3 b. The ring-shaped spacer 25 may be formedof any material with sufficient rigidity, such as a magnetic material ora non-magnetic material. The spacer 25 may be formed of an iron materialsuch as a carbon steel, a magnetic stainless steel, etc. This may makethe spacer 25 act as a magnetic path when the power is applied. This mayresult in reducing magnetic flux density at the root of the magneticpiece 1 of large magnetic flux density, which may be effective forincreasing suction power.

The ring-shaped spacer 25 may alternatively be integrated into themagnetic pole piece 1 to form a one-piece part. Still alternatively, thespacer 25 may be integrated into the second coil holding portion 3 b ofthe bobbin coil to form a one-piece part. These alternatives may serveto reduce the number of parts required.

The waterproof portion 8 is formed to include the waterproof plate 9 andthe resin 10. The magnetic pole piece 1 is extended out of the endsurface of the bobbin 3, and the end surface of the outer yoke 6 isextended out of the end surface of the magnetic pole piece 1. Thewaterproof plate 9 in a shape of a disk is nonmagnetic, the insidediameter of which is smaller in size than the inside diameter of theouter yoke 6. The waterproof plate 9 is formed so that it touches theend surface of the magnetic pole piece 1. Then, a gap 27 is createdbetween the outer yoke 6 and the waterproof plate 9 on the suctionsurface side. The gap 27 is filled with the resin 10 for preventing thecorrosive liquid 17 from entering the inside of the electromagneticactuator 50. Injection, insert molding, etc. may be used as a method offilling the resin 10 in the waterproof plate 9. The waterproof plate 9and the resin 10 form the waterproof portion 8.

Possible materials for the resin 10 may include: polybutyleneterephthalate (PBT), polyphenylene sulfide (PPS), liquid crystallinepolymer (LCP), polyethylene terephthalate (PET), ABS resin, nylon resin,UV resin, etc. The waterproof plate 9 may be formed easily by punching athin plate.

The example of FIG. 1 includes, but not limited to, the waterproofportion 8 where the gap 27 on the suction surface side is filled withthe resin 10. The surface of the electromagnetic actuator 50 may bemolded all over with resin on a stator side, for example, which may makethe electromagnetic actuator 50 highly resistant to corrosion. In thisparticular case, the waterproof portion 8 is not required.

The waterproof portion may alternatively be formed to include thewaterproof cap 30, instead of the waterproof plate 9 and the resin 10,fitted on the suction surface side, as shown in FIG. 5. Possiblematerials for the waterproof cap 30 may include an austenitic stainlesssteel (e.g., JIS SUS304, SUS301, etc) that is nonmagnetic and highlycorrosion resistant. The waterproof cap 30 may be fitted on the suctionsurface side by shrink fitting, press fitting, adhesive fitting, etc. Itis easy to produce the waterproof cap 30 by drawing, etc. The outer yoke6 may be formed almost like the waterproof cap 30 on the reduceddiameter side from the stepped portion 6 a so as to function as thewaterproof cap 30. This may result in reducing the number of partsrequired.

The movable plate storage cap 13 is formed to include the liquid flowinlet portion 15 formed with an opening on the end surface facing themovable plate 12. The movable plate storage cap 13 is filled with thecorrosive liquid 17 inside.

With FIG. 1, the outside diameter of the movable plate 12 is smaller insize than the inside diameter of the movable plate storage cap 13, andalso smaller than the inside diameter of the outer yoke 6.Alternatively, the outside diameter of the movable plate 12 may be madesmaller in size than the inside diameter of the movable plate storagecap 13, but larger than the inside diameter of the outer yoke 6. Then,the following advantages may be achieved: that is, the movable plate 12is allowed to move inside the movable plate storage cap 13, and suctionpower applied between the end surface of the outer yoke 6 and themovable plate 12 is improved (because the gap between the end surface ofthe outer yoke 6 and the movable plate 12 becomes small). This mayresult in increasing suction power.

Possible materials for the movable plate storage cap 13 may include anaustenitic stainless steel (e.g., JIS SUS304, SUS301, etc) that isnonmagnetic and highly corrosion resistant.

The electromagnetic actuator 50 thus formed may achieve high corrosionresistance without losing the suction power.

An austenitic stainless steel may further improve resistance tocorrosion by adding painting such as spray painting, electrostaticpainting, electrophoretic painting, powder painting, etc.

When power is supplied to the receiving end portion 21 from an externalpower source, the electric current flows through the coil 4 to causemagnetic flux to occur. A magnetic path is then formed by the magneticpole piece 1, the bottom yoke 5, the outer yoke 6, and the movable plate12 formed of magnetic materials. Suction power then occurs between theend surface of the magnetic pole piece 1 and the movable plate 12,thereby sucking the movable plate 12 in the corrosive liquid 17.

In this circumstance, the corrosive liquid 17 works as a dumper, whichmay serve to absorb impact caused by the suction of the movable plate12.

When no power is supplied, suction power does not occur. In thiscircumstance, the movable plate 12 floats in the liquid 17. This mayprotect the electromagnetic actuator 50 from abrasion for externalvibration applied. Hence, the electromagnetic actuator 50 may beproduced with excellent durability.

With FIG. 1 and FIG. 5, the movable plate storage cap 13 is fitted tothe outer yoke 6 in order to store the movable plate 12. Alternatively,however, the movable plate storage portion 16 b may be formed on themetal case 16 in replacement of the movable plate storage cap 13, asshown in FIG. 6. In this case, the movable plate storage cap 13 may bereplaced by a rustproof magnetic stainless steel cap 40. The rustproofcap 40 is formed by extending the movable plate storage cap 13 up to theend surface of the outer yoke 6. This may allow the electromagneticactuator 50 to have even higher suction power with the corrosionresistance maintained.

All parts of the electromagnetic actuator 50, other than the magneticpole piece 13 and the rustproof cap 40, may be commonly used. Therefore,all that is needed is to selectively switch the manufacturing processbetween the magnetic pole piece 13 and the rustproof cap 40. This mayallow for automated production, and thereby the electromagnetic actuator50 may be produced with high productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 The figure illustrates a longitudinal section of anelectromagnetic actuator 50, according to a first embodiment.

FIG. 2 The figure illustrates a transverse section of theelectromagnetic actuator where a bobbin coil 2 is not shown, accordingto the first embodiment.

FIG. 3 The figure illustrates a longitudinal section of an iron corewhere a ring-shaped auxiliary sucking portion 20 is additionallyattached to a magnetic pole piece 1, according to the first embodiment.

FIG. 4 The figure illustrates a longitudinal section of an iron corewhere a disk-shaped auxiliary sucking part 20 is additionally attachedto the magnetic pole piece 1, according to the first embodiment.

FIG. 5 The figure illustrates a longitudinal section of theelectromagnetic actuator 50 including a waterproofing portion formedwith a waterproof cap 30, according to the first embodiment.

FIG. 6 The figure illustrates a longitudinal section of theelectromagnetic actuator 50 where a movable plate storage portion 16 bis formed on a metal case 16, according to the first embodiment.

EXPLANATION OF REFERENCE NUMERALS

-   1 magnetic pole piece-   2 bobbin coil-   3 bobbin-   3 a first coil holding portion-   3 b second coil holding portion-   4 coil-   5 bottom yoke-   6 outer yoke-   6 a stepped portion-   7 lead wire outlet portion-   8 waterproof portion-   9 waterproof plate-   10 resin-   11 gap-   12 movable plate-   13 movable plate storage cap-   14 space-   15 liquid flow inlet portion-   16 metal case-   16 a opening-   17 liquid-   20 auxiliary sucking portion-   21 power receiving unit-   22 terminal block-   23 terminal pin-   24 connection space-   25 spacer-   27 gap-   30 waterproof cap-   40 rustproof cap-   50 electromagnetic actuator

1. An electromagnetic actuator, which is incorporated into a deviceusing a corrosive liquid, comprising: a magnetic pole piece in a shapeof a pillar; an outer yoke in a shape of a tube that is corrosionresistant, and that is placed around a periphery of the magnetic polepiece; a bottom yoke that connects the magnetic pole piece and one endportion of the outer yoke; a bobbin coil that is attached to themagnetic pole piece, the bobbin coil including a first coil holdingportion, and a second coil holding portion on a bottom yoke side; astepped portion that is formed on an outer surface of the outer yoke tomake a diameter on an opposite side to the bottom yoke smaller than adiameter on the bottom yoke side; a waterproof portion that prevents thecorrosive liquid from entering at least where the bobbin coil and themagnetic pole piece are; a movable plate that is placed in the corrosiveliquid to form a magnetic circuit together with the magnetic pole piece,the outer yoke, and the bottom yoke, wherein the movable plate is storedin a space into which the corrosive liquid flows from the device usingthe corrosive liquid, the space being separated from at least the bobbincoil and the magnetic pole piece by the waterproof portion and beingcreated either inside the electromagnetic actuator, or between thedevice using the corrosive liquid and the electromagnetic actuator, andwherein the outer yoke is incorporated into the device using thecorrosive liquid, on a reduced diameter side from the stepped portion.2. The electromagnetic actuator of claim 1, wherein the waterproofportion includes a waterproof cap in a shape of a cap that is fitted tothe outer surface of the outer yoke on the reduced diameter side, andattached against another end portion of the outer yoke and an endportion of the magnetic pole piece on the opposite side to the bottomyoke, the electromagnetic actuator further comprising: a movable platestorage cap in a shape of a cup that is fitted to an outer surface ofthe waterproof cap to create said space between the waterproof cap andthe movable plate storage cap, and formed to create an opening on asurface facing the end portion of the magnetic pole piece on theopposite side to the bottom yoke.
 3. The electromagnetic actuator ofclaim 1, wherein the waterproof portion includes a waterproof plate thatis attached against an end portion of the magnetic pole piece on anopposite side to the bottom yoke, and formed to create a gap between thefirst coil holding portion and an inner surface of the outer yoke, theelectromagnetic actuator further comprising: a rustproof cap in a shapeof a cup that is fitted to the outer surface of the outer yoke on thereduced diameter side, and attached against another end portion of theouter yoke, and formed to include an opening whose diameter isapproximately same in size as an inside diameter of the outer yoke,wherein said space is created in a lower portion of the waterproof platebetween the device using the corrosive liquid and the electromagneticactuator.
 4. The electromagnetic actuator according to claim 1, whereinthe magnetic pole piece and the bottom yoke are formed of an ironmaterial, and the outer yoke is formed of a stainless steel.
 5. Theelectromagnetic actuator according to claim 4, wherein a cross-sectionalarea of the outer yoke is larger than a cross-sectional area of themagnetic pole piece.
 6. The electromagnetic actuator according to claim4, wherein the outer yoke formed of the stainless steel is painted. 7.The electromagnetic actuator according to claim 1, wherein the outeryoke is formed of an iron material and painted.
 8. The electromagneticactuator according to claim 1 further comprising: a spacer in a shape ofa ring that is closely attached to an end surface of the second coilholding portion at a root of the magnetic pole piece on the bottom yokeside, for positioning and securing the bobbin coil.
 9. Theelectromagnetic actuator according to claim 8, wherein the bobbin coilincludes a power receiving unit that supplies power to the second coilholding portion, and wherein the power receiving unit is placed in aconnection space that is created between the second coil holding portionand the bottom yoke.
 10. The electromagnetic actuator according to claim9, wherein the power receiving unit includes a terminal block and twoterminal pins that are mounted on the terminal block.
 11. Theelectromagnetic actuator according to claim 10, wherein the two terminalpins are joined and connected, respectively, with the bobbin coil at awinding start portion and a winding end portion by soldering, etc. thatmelts a film of the coil.
 12. The electromagnetic actuator according toclaim 10, wherein the second coil holding portion includes a hangingportion formed on an outer surface, on which a coil end extending overto the terminal pins is hung.
 13. The electromagnetic actuator accordingto claim 1 further comprising: an auxiliary sucking portion that isformed at an end portion of the magnetic pole piece on the opposite sideto the bottom yoke to increase an area of the end portion.
 14. Theelectromagnetic actuator according to claim 13, wherein the auxiliarysucking portion is formed of one of a ring-shaped magnetic material anda disk-shaped magnetic material.
 15. The electromagnetic actuatoraccording to claim 13, wherein a relation La>2Lg is satisfied where Larepresents a distance between an outside diameter of the auxiliarysucking portion and an inside diameter of the outer yoke, and Lgrepresents a gap between the movable plate and one of the auxiliarysucking portion and the magnetic pole piece.
 16. The electromagneticactuator according to claim 1, wherein the magnetic pole piece, thebottom yoke, and the outer yoke are separate piece parts.
 17. Theelectromagnetic actuator according to claim 1, wherein the magnetic polepiece and the bottom yoke are formed into one piece part when themagnetic pole piece and the bottom yoke are formed of a same materialand the outer yoke is formed of a different material.
 18. Theelectromagnetic actuator according to claim 1, wherein the bottom yokeand the outer yoke are formed into one piece part when the bottom yokeand the outer yoke are formed of a same material and the magnetic polepiece is formed of a different material.
 19. The electromagneticactuator according to claim 1, wherein the magnetic pole piece, thebottom yoke and the outer yoke are formed into one piece part when themagnetic pole piece, the bottom yoke and the outer yoke are formed of asame material.
 20. An electromagnetic actuator comprising: a magneticpole piece in a shape of a pillar; an outer yoke in a shape of a tubethat is corrosion resistant, and that is placed around a periphery ofthe magnetic pole piece; a bottom yoke that connects the magnetic polepiece and one end portion of the outer yoke; a bobbin coil that isattached to the magnetic pole piece, the bobbin coil including a firstcoil holding portion, and a second coil holding portion on a bottom yokeside; a waterproof plate that is attached against an end portion of themagnetic pole piece on an opposite side to the bottom yoke, and formedto create a gap among the first coil holding portion, an inner surfaceof the outer yoke and the waterproof plate; a stepped portion that isformed on an outer surface of the outer yoke to make a diameter on theopposite side to the bottom yoke smaller than a diameter on the bottomyoke side; a movable plate storage cap in a shape of a cup that isfitted to the outer surface of the outer yoke on a reduced diameterside, attached against another end portion of the outer yoke to create aspace between the waterproof plate and the movable plate storage cap,and formed to create an opening on a surface facing the waterproofplate; a movable plate that is placed in the space between thewaterproof plate and the movable plate storage cap; and a resin that isfilled in a gap formed between the outer yoke and the waterproof plate,wherein the reduced diameter side from the stepped portion isincorporated into the device using the corrosive liquid.